Beam splitter

Abstract

A beam splitter formed by laminating a plurality of optical films on a glass substrate having a refractive index of 1.51+/-0.10. The optical films are first, second, third, fourth, and fifth layers laminated in this order from the glass substrate. The first layer has a refractive index of 1.44+/-0.10 and an optical film thickness of 0.05-0.15; the second layer has a refractive index of 1.68+/-0.10 and an optical film thickness of 0.01-0.10; the third layer has a refractive index of 1.44+/-0.10 and an optical film thickness of 0.50-0.60; the fourth layer has a refractive index of 2.23+/-0.10 and an optical film thickness of 0.25-0.35; and the fifth layer has a refractive index of 1.44+/-0.10 and an optical film thickness of 0.25-0.35. The optical film thickness means a relative value represented by n x d/ lambda where n denotes a refractive index; d denotes an actual film thickness, and lambda denotes a wavelength deciding the center of a wavelength band. The beam splitter can reduce the polarization dependency of a branching ratio with a beam incident angle of 22.5 DEG .

What is claimed is: 
     
       1. A beam splitter formed by laminating a plurality of optical films on a substrate, wherein: said substrate comprises a glass substrate having a refractive index of 1.51±0.10; and   said optical films comprise:   a first layer formed on said glass substrate, said first layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.40-0.50;   a second layer formed on said first layer, said second layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.40-0.50;   a third layer formed on said second layer, said third layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.30-0.40;   a fourth layer formed on said third layer, said fourth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.10-0.20;   a fifth layer formed on said fourth layer, said fifth layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.10-0.20;   a sixth layer formed on said fifth layer, said sixth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.10-0.20;   a seventh layer formed on said sixth layer, said seventh layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.10-0.20;   an eighth layer formed on said seventh layer, said eighth layer having a refractive index of 1.44-0.10 and an optical film thickness of 0.20-0.30;   a ninth layer formed on said eighth layer, said ninth layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.55-0.65;   a tenth layer formed on said ninth layer, said tenth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.40-0.50;   an eleventh layer formed on said tenth layer, said eleventh layer having a refractive index of 2.23±0.10 and an optical film thickness of 2.50-3.50; and   a twelfth layer formed on said eleventh layer, said twelfth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.20-0.30.   
     
     
       2. A beam splitter according to claim 1, wherein: said first layer, said third layer, said fifth layer, said seventh layer, said ninth layer, and said eleventh layer are deposited films formed of TiO 2  or Ta 2  O 5  ; and   said second layer, said fourth layer, said sixth layer, said eighth layer, said tenth layer, and said twelfth layer are deposited films formed of SiO 2 .   
     
     
       3. A beam splitter formed by laminating a plurality of optical films on a substrate, wherein: said substrate comprises a glass substrate having a refractive index of 1.51±0.10; and   said optical films comprise:   a first layer formed on said glass substrate, said first layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.39-0.50;   a second layer formed on said first layer, said second layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.40-0.50;   a third layer formed on said second layer, said third layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.27-0.40;   a fourth layer formed on said third layer, said fourth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.07-0.20;   a fifth layer formed on said fourth layer, said fifth layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.09-0.20;   a sixth layer formed on said fifth layer, said sixth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.10-0.20;   a seventh layer formed on said sixth layer, said seventh layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.13-0.23;   an eighth layer formed on said seventh layer, said eighth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.20-0.33;   a ninth layer formed on said eighth layer, said ninth layer having a refractive index of 2.23±0.10 and an optical film thickness of 0.50-0.65;   a tenth layer formed on said ninth layer, said tenth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.30-0.50;   an eleventh layer formed on said tenth layer, said eleventh layer having a refractive index of 2.23±0.10 and an optical film thickness of 2.40-3.50; and   a twelfth layer formed on said eleventh layer, said twelfth layer having a refractive index of 1.44±0.10 and an optical film thickness of 0.19-0.30.   
     
     
       4. A beam splitter according to claim 3, wherein: said first layer, said third layer, said fifth layer, said seventh layer, said ninth layer, and said eleventh layer are deposited films formed of TiO 2  or Ta 2  O 5  ; and   said second layer, said fourth layer, said sixth layer, said eighth layer, said tenth layer, and said twelfth layer are deposited films formed of SiO 2 .